Individuals are very varied, so a lot needs to be adapted to an particular class.
Youngest children: no text activties. Everything should be structured as a game. Short attention spans, so each activity must be short. Probably still learning their native language, so can work very well with all instructions in target language.
Elementary school age: Increasing ability to work with text. Can start to do some more formal work (such as "gap filling"). In the "grammar gap" at which time they are too old to pick up grammar quickly as a native speaker does, but to young to learn grammar formally as an older learner can. Still a good mix of games is important. Still largely motivated by "fun".
Secondary school: External motivations such as "tests" become more important. Most can now work with texts effectively (but look out for undiagnosed dyslexia) Can be resistant to speaking in a foreign language. More able to take correction, can begin to learn about the target language. Longer activities, perhaps just "starter/main/plenary" become possible. These students understand "school". Building a good teacher/student relationship is difficult but important. You need to be very aware of them.
Adults: Wide range of motivations. Some will just want conversation, others will be aiming towards particular tests. Most will want something different from "school". Can discuss aims and preferences more directly. Much more willing to speak than school children.
Generally, you should be building up a range of resources. It is worth spending a little to get some books, especially if you get a good series that comes with teachers' guides. Even if you don't always (or ever) use the textbook in class, it gives you ideas and sparks to your own creativity.